Resistance, Capacitance, Inductance, and Impedance

To understand what factors affect the formation, transmission, amplification, and detection of a detector signal, it is important to comprehend the function of resistance, capacitance, inductance, and impedance, which are the basic constituents of any electronic circuit. For this reason, a brief review of these concepts is offered. 

The resistance / is a measure of how difficult (or easy) it is for an electric current to flow through a conductor. The resistance is defined by Ohm s law as the ratio of a voltage to current flowing through a conductor (Fig. 10.1a). The resistance is measured in ohms (ft). If a potential difference of 1 V generates a current of 1 A, the resistance is 1 ft that is, 

Capacitance C is the ability to store electrical charge. A capacitor usually consists of two conductors separated by an insulator or a dielectric (Fig. 10.lb). Every conductor, e.g., simple metal wire, has a certain capacitance. The capacitance is measured in farads (F). If a charge of 1 coulomb produces a potential difference of 1 V between the two conductors forming the capacitor, then its capacitance is 1 F that is, 

If the voltage across the capacitor is constant, no current flows through it i.e., a capacitor acts as an open circuit to dc voltage. If, however, the voltage changes, a current flows through the capacitor equal to 

Capacitance and inductance are important for time-varying signals. To be able to introduce and discuss the pertinent concepts, consider a sinusoidal voltage signal with maximum voltage and frequency o) applied to an RC circuit, as shown in Fig. 10.2  

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